Hi everyone, so after replacing many parts and qualifying all voltage rails on the KLM596 board, I fired it up and the display is not turning on. I swapped the original KLM596 board with a spare and the display comes on, so I know the connector/harness and display board are good. I checked all timing signals / address lines from the CPU to the 81c55 with my scope and they are present on the 81c55 but there is no output on PC and PB ports or T/O, so i suspect its b/o unless something is loading it down? any suggestions? all traces and lines were qualified between IC24-IC25-IC30-IC31.
The IC is marked as MSM81c55RS, do I need an exact replacement or will any other variations do?
thank you